Theoretically, this process can go on indefinitely, effectively rendering the jellyfish biologically immortal,[3][6] although in practice individuals can still die. In nature, most Turritopsis dohrnii are likely to succumb to predation or disease in the medusa stage without reverting to the polyp form.[7] --WP
Cicadas, right?
The... (don't quote me on this) 13yr and 17yr stages are both endangered now, as I understand it. The years refer to how long the larvae develop underground, then strategically arise in order to make predation upon them difficult to predict by other animals, primarily wasps.
Locusts refer to some species of grasshoppers that mass in to incredible numbers, retaining their wings, right? Crop-killers IIRC.